1. Field of the Invention
The present invention relates generally to a conveyer system and more particularly is directed to a new and improved accumulating conveyer capable of conveying loads having a wide range of predetermined weights, including heavy loads, and accumulating them either against each other (i.e., load-to-load or column accumulation) or in spaced relation to each other (i.e., zone accumulation).
2. Description of the Prior Art
Accumulating conveyers of various types are known in the prior art. Prior art conveyers suitable for carrying relatively heavy loads are generally of one of two types: roller flight conveyers and reciprocating gravity accumulating conveyers. Roller flight conveyers utilize rollers which are freewheeling and which only rotate by inertia when a load passes over them. The entire set of rollers, in a manner resembling an endless belt driven between two pulleys, is moved in a direction transverse to the axes of the rollers thereby carrying the loads along. Disadvantages of the roller flight type conveyers include the inability to vary the end pressure (i.e., the pressure which builds up as loads accumulate against each other) and the difficulty of using such conveyers to zone accumulate. Reciprocating gravity accumulating conveyers, the second type of conveyer presently used to convey heavy loads, operate by shuttling freewheeling rollers back and forth while the loads move by gravity. Conveyers of this type have the disadvantage of being incapable of zone accumulating. Further disadvantages of reciprocating gravity accumulating conveyers are that such conveyers require a change in elevation between the ends of the conveyer and that such conveyers can transport loads only in the downhill direction.
Various types of conveyers in which the rollers are driven or rotated to cause the loads in contact with the rollers to be conveyed are also known in the prior art. Many of the drive mechanisms for rotating rollers in such prior art conveyers are either unsuitable for driving rollers when heavy loads are to be conveyed or are unsuitable for use in accumulating conveyer systems. The drive mechanisms for accumulating conveyers utilize various types of clutch mechanisms to permit the rollers to cease rotating when the load comes to a halt (e.g., at the end of the conveyer). It is also known to employ in a roller conveyer driven rollers wherein a rotary load-engaging roller portion is in permanent frictional engagement with a driving portion. In such prior art conveyers, however, the permanent frictional engagement between such portions causes overheating and considerable wear so that the magnitude of forces with which the driving portion transmits torque to the driven portion varies in response to several factors, including progressive wear on such portions. Overheating can cause excessive frictional engagement between driving and driven portions so that the driven portion continues to rotate when the load is at a standstill or so that the load travels with reference to the driven portion when it is desired to advance the load at a speed which is higher than the speed transmitted thereto by the driving portion when the driven portion rotates with the driving portion. One example of a conveyer in which rollers are driven by frictional engagement between a driving portion and a driven portion is described in U.S. Pat. No. 4,111,087 issued to Pankratz et al. (see FIG. 4 and col. 5, lines 32-61 of the Pankratz et al. patent).
The present invention utilizes a drive mechanism of the type in which a rotary load-engaging roller portion is in permanent frictional engagement with a driving portion. However, by use of a friction pad, the present invention overcomes the problems of overheating and excessive frictional engagement which exist with prior art devices. The present invention provides a drive mechanism particularly suitable for rotating rollers in an accumulating conveyer system for conveying a wide range of loads, including relatively heavy loads.